← Back to Communities

Geobacter-Methanosaeta DIET Community

Community ID CommunityMech:000032
Ecological State STABLE
Environment sediment
ENVO:00002007

A syntrophic two-member consortium consisting of Geobacter metallireducens and Methanosaeta harundinacea that performs direct interspecies electron transfer (DIET) during ethanol oxidation. G. metallireducens oxidizes ethanol and transfers electrons directly to M. harundinacea via electrically conductive pili and aggregates, bypassing the need for diffusible electron carriers like H2 or formate. M. harundinacea uses these electrons to reduce CO2 to methane. This coculture forms conductive aggregates and achieves stoichiometric conversion of ethanol to methane via DIET. Unlike hydrogen-mediated syntrophy, DIET relies on biological electrical connections between cells, with conductive aggregates serving as conduits for long-range electron transfer. M. harundinacea is an obligate acetoclastic methanogen that can also accept electrons via DIET for CO2 reduction, making it unique among acetoclastic methanogens in supporting direct electron transfer mechanisms.

Taxonomy

Taxon Ontology ID Functional Roles Abundance
Geobacter metallireducens NCBITaxon:28232
PRIMARY_DEGRADER SYNTROPHIC_PARTNER
N/A
  • doi:10.1039/C3EE42189A - SUPPORT (IN_VITRO)
    "This possibility was further investigated in defined co-cultures of Geobacter metallireducens and Methanosaeta harundinacea which stoichiometrically converted ethanol to methane"
Methanosaeta harundinacea NCBITaxon:301375
SYNTROPHIC_PARTNER
N/A
  • doi:10.1039/C3EE42189A - SUPPORT (IN_VITRO)
    "This possibility was further investigated in defined co-cultures of Geobacter metallireducens and Methanosaeta harundinacea which stoichiometrically converted ethanol to methane"

Ecological Interactions

Ecological interaction network for Geobacter-Methanosaeta DIET Community Bipartite graph where circle nodes represent taxa and each ecological interaction is drawn as a distinct non-circular symbol, with colour repeating the same distinction (mutualism, syntrophy).
Taxon
Mutualism
Syntrophy

Ethanol Oxidation and Direct Electron Transfer

SYNTROPHY

Source Taxon: Geobacter metallireducens

Metabolites: ethanol (CHEBI:16236), acetate (CHEBI:30089)

Biological Processes:

Downstream Effects:
→ Direct Electron Acceptance and Methanogenesis

Evidence

  • doi:10.1039/C3EE42189A - SUPPORT (IN_VITRO)
    "Furthermore, Geobacter species, the most abundant bacteria in the aggregates, highly expressed genes for ethanol metabolism and for extracellular electron transfer via electrically conductive pili, suggesting that Geobacter and Methanosaeta species were exchanging electrons via direct interspecies electron transfer (DIET)"

Direct Electron Acceptance and Methanogenesis

MUTUALISM

Source Taxon: Methanosaeta harundinacea

Metabolites: methane (CHEBI:16183), carbon dioxide (CHEBI:16526)

Biological Processes:

Evidence

  • doi:10.1039/C3EE42189A - SUPPORT (IN_VITRO)
    "Furthermore, Geobacter species, the most abundant bacteria in the aggregates, highly expressed genes for ethanol metabolism and for extracellular electron transfer via electrically conductive pili, suggesting that Geobacter and Methanosaeta species were exchanging electrons via direct interspecies electron transfer (DIET)"

Knowledge gaps & discussions (1)

KNOWLEDGE_GAP OPEN Alongside DIET-driven CO2 reduction, does M. harundinacea also cross-feed on the acetate generated by G. metallireducens ethanol oxidation, and what fraction of methane comes from each route in this defined coculture?

A causal-graph pass on this record proposed an additional acetate cross-feeding node and an acetate -> methanogenesis edge, on the reasoning that Methanosaeta is classically an acetoclastic genus and that ethanol oxidation by G. metallireducens yields acetate, giving an overall stoichiometry near 1.5 mol CH4 per mol ethanol. That claim is NOT curated here as an interaction: the primary source (doi:10.1039/C3EE42189A) is cached abstract-only and its full text was not retrievable, and the abstract states only that M. harundinacea "accepted electrons via DIET for the reduction of carbon dioxide to methane" - it does not report acetate cross-feeding, the acetate/DIET split, or the per-route methane stoichiometry. The supporting quotations offered for the acetate route came from secondary reviews attributing findings to this study, which per this repo's conservative-curation rule (see CommunityMech:000176) is not a sufficient basis for an exact-system causal edge. Resolving this needs the primary full text or a radiotracer/isotope partition experiment in this exact coculture.

Attaches to: ecological_interactions#Ethanol Oxidation and Direct Electron Transfer, ecological_interactions#Direct Electron Acceptance and Methanogenesis

1 evidence item(s)
IN_VITRO PARTIAL doi:10.1039/C3EE42189A

Transcriptomic, radiotracer, and genetic analysis demonstrated that M. harundinacea accepted electrons via DIET for the reduction of carbon dioxide to methane

The abstract demonstrates only the DIET/CO2-reduction route; it is silent on an acetate cross-feeding route, which is why that edge is filed as a gap rather than curated.

Environmental Factors

Factor Value Unit
Anaerobic Conditions Strict anaerobic N/A
  • doi:10.1039/C3EE42189A - SUPPORT (IN_VITRO)
    "This possibility was further investigated in defined co-cultures of Geobacter metallireducens and Methanosaeta harundinacea which stoichiometrically converted ethanol to methane"
Conductive Aggregate Formation Required for DIET N/A
  • doi:10.1039/C3EE42189A - SUPPORT (IN_VITRO)
    "Furthermore, Geobacter species, the most abundant bacteria in the aggregates, highly expressed genes for ethanol metabolism and for extracellular electron transfer via electrically conductive pili, suggesting that Geobacter and Methanosaeta species were exchanging electrons via direct interspecies electron transfer (DIET)"
Pili Expression Essential for DIET initiation N/A
  • doi:10.1039/C3EE42189A - SUPPORT (IN_VITRO)
    "Furthermore, Geobacter species, the most abundant bacteria in the aggregates, highly expressed genes for ethanol metabolism and for extracellular electron transfer via electrically conductive pili, suggesting that Geobacter and Methanosaeta species were exchanging electrons via direct interspecies electron transfer (DIET)"

Growth Media

Modified Freshwater Medium for DIET Coculture (CultureMech:015435)

View in CultureMech →

Temperature 37 °C
Atmosphere ANAEROBIC

Composition

Component Concentration Unit CHEBI
Ethanol 20 mM CHEBI:16236
L-Cysteine 1 mM CHEBI:17561
Sodium sulfide nonahydrate 0.5 mM CHEBI:76209

Preparation notes: Modified freshwater medium boiled to reduce oxygen solubility, then cooled under N2/CO2 (80:20) gas mixture. Ethanol (20 mM) and other additives added from anaerobic sterile stocks: 1 mM cysteine and 0.5 mM Na2S·9H2O as reducing agents. Bicarbonate/CO2 serves as sole electron acceptor. Vitamins included per standard formulation. Cultures grown in 10 mL anaerobic pressure tubes or serum bottles; larger studies used 50 mL medium in 160 mL serum bottles. Sampling performed with N2/CO2 (80:20) degassed hypodermic syringes. Digesters operated at 37°C mesophilic conditions.

Evidence

doi:10.1039/C3EE42189A

"This possibility was further investigated in defined co-cultures of Geobacter metallireducens and Methanosaeta harundinacea which stoichiometrically converted ethanol to methane"